PTEN is a tumor suppressor for gliomas and many other tumor types. PTEN encodes a phosphatase specific for phosphatidylinositol phosphate (PIP) and reverses the action phosphatidylinositol 3-kinase (P13K). Although P13K is a well studied regulator of neuronal survival, our recent publication (Lachyankar et al., Appendix) was the first to propose a role for PTEN in the nervous system. We found that PTEN is expressed by neurons in adult brain. In cell culture models, PTEN is expressed during neurotrophin-induced differentiation and is detected in both cytoplasm and nucleus. Suppression of PTEN levels with antisense oligonucleotides leads to death of immature neurons during neurite extension. These results provide the basis for this application. In Sp. Aim 1, we will determine the mechanism by which nerve growth factor (NOF) regulates PTEN levels. We do not observe significant changes in PTEN mRNA levels during NGF-induced differentiation. We will test the hypothesis that NGF induces PTEN protein by altering the rate of translation or the rate of degradation of PTEN. The latter is a particularly appealing possibility because PTEN has two PEST sequences and turns over rapidly. For Sp. Aim 2, we will analyze the nature and function of PTEN in the nucleus. We will identify nuclear localization signals associated with PTEN, any secondary modifications of nuclear PTEN, and the relation of PTEN with nuclear PIPs and other nuclear domains. In Sp. Aim 3, we will test whether P13K and PTEN are the controlling enzymes for PIP levels. We also will examine the role of two other PIP phosphatases, SHIP and synaptojanin. We will determine whether PIPs provide feedback regulation of PTEN, and whether PTEN action is associated with subcellular compartments of the neuron. These experiments address how PTEN and, in turn, PIPs regulate development, neuronal survival, neurodegeneration, and development of brain tumors.